Top physics at CDF

Koji Nakamura on behalf of CDF collaboration

"New Developments of Flavor Physics"

March 9th, 2009

Top Quark at Tevatron What is top quark?

Evidenced in 1994 by CDF, discovered in 1995 by Tevatron

The heaviest quark so far. The Mass is about 172 GeV. Now We have much more data to analyze top quark

properties.

24 Aug, 2008

Record : 3.8 fb-1

Good Data: 3.2 fb-1

Top Quark at Tevatron What is top quark?

Evidenced in 1994 by CDF, discovered in 1995 by Tevatron

The heaviest quark so far. The Mass is about 172 GeV. Now We have much more data to analyze top quark

properties.MassCharge

Production Cross SectionFwd-Bwd AsymmetryProduction Mechanism

W helicity

New Physics FCNC ttbar resonance charged Higgs ……

Top Quark properties in pair production

30% : 70%

Top Quark at Tevatron

~ 6.7 pb

~ 2.9 pb

What is top quark? Evidenced in 1994 by CDF, discovered in 1995 by

Tevatron The heaviest quark so far. The Mass is about 172 GeV.

Now We have much more data to analyze top quark properties.Single top production is allowed in SM

Singletop production

Both CDF and D0 Submitted to PRL CDF

DØarXiv.org:0903.0885

arXiv.org:0903.0880

Lumi : 3.2 fb-1Expected : 5.9 σObserved : 5.0 σ

Lumi : 2.3 fb-1Expected : 4.5 σObserved : 5.0 σ

Observation

Observation

Why Single Top Quark?

Production rate is proportional to |Vtb|2

t = (1.98 ± 0.25) |Vtb|2 pb

s = (0.88 ± 0.11) |Vtb|2 pb

Top Polarization study

Probe Non Standard Model phenomena

Single top quarks are 100% polarized in SM Can test this with angular distribution of top decay

Can search for heavy W’ boson or H±

Technical MotivationTest of the methodology for Higgs search (the same final state as the WHlνbb signal)

2 or 3 high Pt jets (Pt>20 GeV)

One high Pt lepton (Pt>20 GeV) Large

Missing Energy (Et>25 GeV)

Event topology

difficulty

Singletop production with decay into lepton + 2 jets final state

Singletop

Top pair

Signal is hidden under the huge bkg

Multivariate analyses are needed

Dominant process of 4 jets bincounting method is possible

Background (at least 1 b-tag)

Analysis strategy CDF Data Set Signal Model Background Model

Event Selection

Likelihood Function

Multivariate Analysis

Blind analysis

Split in sub setof different purity

Cross section measurementD

iscrimin

an

t

|Vtb| measurement

Significance and xsec limit

Lepton Trigger Event Met + Jets Trigger Event

Neural Network

Matrix Element

Boosted Decision Tree

Non triggered lepton No lepton

Neural Network

Multivariate Analysis

Lep+jets

Likelihood AnalysisUsed projective likelihood function to combine the separation power of several variables.

t-channel optimized analysis s-channel optimized analysisExample of input variables

2 b-tag events OnlyExample of input variables

HTQ*η pTMlνb

Result of Likelihood Analyses t-channel optimized analysis s-channel optimized analysis

pb 1.6σ 0.80.7ts

pb 1.5σ 0.9

0.8s

Expected significance: 4.1 σObserved significance: 2.4 σ

Expected significance: 1.1 σObserved significance: 2.0 σ

s- and t-channel are the signal s-channel is the signal

2 b-tag events Only

Combination of Likelihood Analyses

To obtain s- and t-channel cross section in s-t plane,We perform s- and t-channel cross section fit simultaneously.

Combine following 2 analyses: 1-b-tag events -- optimized to t-channel 2-b-tag events -- optimized to s-channel

pb 1.0σ

pb 1.4σ

t

s

Matrix Element Analysis

Using Matrix Element information to calculate probabilities for seven different underlying processes: s-channel, t-channel, Wbb, tt, Wcc, Wc+jet and Wgg.

pb 2.5σ 0.70.6ts

Expected significance: 4.9 σObserved significance: 4.3 σ

Result of ME Analysis

The other MV TechniquesNeural Network analysis Boosted Decision Tree analysis

Sequence of binary splits using the discriminating variable which gives best sig-bkg separation.

An orthodox NN analysis using Neuro Bayes Program 18-25 variables are used

pb 0.61.8σ ts

Expected significance: 5.2 σObserved significance: 3.5 σ pb 2.1σ 0.7

0.6-ts

Expected significance: 5.2 σObserved significance: 3.5 σ

Result of NN and BDT analyses Neural Network analysis Boosted Decision Tree analysis

Combination : 5 lep+jets analysis

Discriminant outputs from analyses (LFT, LFS, ME, NN, BDT ) are combined into a single, more powerful super discriminant (SD) using neural networks(NEAT).

pb 2.1σ 0.60.5-ts

Expected significance:

> 5.9 σObserved significance:

4.8 σ

MET+jets without lepton channel

Using no Lepton events by MET+jets Trigger.Independent sample from lepton+jets analysis.Using NN based event selection and NN based discriminant. Challenging!! Huge QCD background…

pb 4.9σ 2.52.2-ts

Expected significance: 1.4 σObserved significance: 2.1 σ

CDF Combination and Singletop Conclusion

Finally, we combined Super Discrimant analysis and no Lepton analysis.

Expected significance: > 5.9 σObserved significance: 5.0 σ

|Vtb|=0.91± 0.11 (exp.) ± 0.07 (theory)

Assuming no anomalous coupling 2SM

tbSM

measured2measuredtb |V|

σσ

|V|

|Vtb|>0.71(95% CL)

pb 2.3σ 0.60.5-ts

Cross section:

|Vtb| calculation:

ttbar propertiesL>=2.7 fb-1 result only(second half of 2008 and 2009)

Top Quark Mass Measurement Top Quark production cross section W helicity Forward Backward asymmetry ttbar production mechanism Search for the FCNC top decay Search for the stop Mimicking Top Event Signatures Search for charged higgs in top decay Search for the t’ quark ……

backup

Most of analysis fit the top quark mass with in-situ JES systematic.

The uncertainty of the top mass result is already systematic dominant.

0.85% precision 10% improved We need reconsidering systematics.

e.g. New Systematic Uncertainty Color Reconnection: A Variation of the Phenomenological description of color reconnection between final state particles.

M top = (172.6 ± 0.9stat ± 1.2syst) GeV/c 2

Added here for the First Time !!

Top Mass measurement Combination

Top Mass measurement New ResultTemplate Method 3.0fb-1 : l+jets

Mtop = 171.8 ± 1.5 (stat.+JES) ± 1.1 (syst.) GeV/c2

M top = (172.1 ± 7.9stat ± 3.0syst) GeV/c

2

Lepton Pt 2.7 fb-1

Mtop = 171.8 ± 0.9 (stat.) ± 0.7 (JES) ± 1.1 (syst.) GeV/c2

Δ JES =

0.4

0 ±

0.26

σ

Matrix Element 3.2fb-1

Mtop = 174.8 ± 1.7(stat.) ± 1.9(syst.) GeV/c2

All Had. 2.9fb-1 : template with NN selection

Top Cross section Combination @Mtop=175 GeV

σpre = 6.7 ± 0.8stat ± 0.4syst ± 0.4lumi pb.

Di-lepton : 2.8 fb-1

σtag = 7.8 ± 0.9stat ± 0.7syst ± 0.4lumi pb.

σttbar = 7.08 ± 0.38 (stat) ± 0.36 (syst) ± 0.41 (lumi) pb

Lepton+jets with NN : 2.8 fb-1

Uncertainty is dominated by Luminosity Using ratio of σttbar/σZ 6%(lumi)->2%(theory)

http://www-d0.fnal.gov/Run2Physics/top/http://www-cdf.fnal.gov/physics/new/top/top.html

Following pages describe more detail

Backup

dileptons6%had+e/μ

4%

lepton+jets34%

had+jets10%

all jets46%

Top Quark Decay Product

Jet Clustering and energy correction

Clustering

Summing tower energies in ΔR( ) =0.422 φη

Correction

Relative correctionMinimum bias correctionAbsolute value correctionUnderling event correctionOut of cone correction

New Physics Phenomena in s-t plane

<<

SM |Vtb|<1

(+)

SM H±,W’

S-channel optimization search

t-channel s-channel top pair

Tevatron 1.98 pb 0.88 pb 6.7 pb

LHC 250 pb 11 pb 870 pb

It is possible to search s-channel using 2-b-tag information

Sensitive to the new physics mainly theory with extra boson(W’,H±)

Exactly the same final state as: WH->lνbb (Golden channel at Tevatron)

It is difficult to search s-channel at LHC because…

Background Estimation

(non W)

MC basedQCD(nonW) Modeled by - failed electron - non isolated muon - jet trigger event

W+jetsPre-b-tag events

fixed

Missing Et

data

2b-tagged events

b-taggingW+jets : mistag weightW+bb, W+cc : HF fraction

QCD(nonW) x mistag weight

The number of event prediction

Acceptance Gain for Muon

Non-triggerd muon in Met+2Jets Trigger

Muon Trigger event

Lepton trigger requires CMU&CMP (CMUP) or CMX

-> add CMU only, CMP only and so on…

Single top @ CDF Acceptance +30% Significance +15%

Systematic Uncertainty

Top Mass measurement with in-situ W->jj JES calibration

1 tag

2 tag

Mtop MjjTemplate Method

Mtop = 171.8 ± 1.5 (stat.+JES) ± 1.1 (syst.) GeV/c2

Mtop = 171.8 ± 0.9 (stat.) ± 0.7 (JES) ± 1.1 (syst.) GeV/c2

ΔJES = 0.40 ± 0.26 σ

Matrix element (Multi-variate) Method

Top Mass : Lepton Pt 2.7 fb-1

Muon dataElectron data

M top = (172.1 ± 7.9stat ± 3.0syst) GeV/c 2

Top Mass : All hadronic 2.9 fb-1

Mtop

Mjj

1 tag 2 tag

Mtop = 174.8 ± 1.7(stat.) ± 1.9(syst.) GeV/c2

Summer 2008 Tevatron Future Precision & EWK fit.

σZtheory = 251.3 ± 5.0 (sys) pb

σz measured=  253.27 ± 1.01(stat) +4.4-4.6 (sys) +16.63

-13.71 (lumi) pb

1/R = σZ /σttbar =  36.47 +2.06-2.29 (stat) +1.88-

1.96(sys)

ttbar cross section using Ratio σttbar/σZ

σ ttbarmeasured =6.89 ± 0.41(stat) +0.41

-0.37(sys) ± 0.14 (theory) pb

σ ttbarmeasured =1/R x σZ

theory

σttbarmeasured = 7.08 ± 0.38 (stat) ± 0.36 (syst) ± 0.41

(lumi) pb

W helicity 1.9 fb-1

the angle between the lepton as measured in the W rest frame and the W boson as measured in the top rest frame

F+ = -0.04 ± 0.04(stat) ± 0.03(syst)

F0= 0.59 ± 0.11(stat) ± 0.04 (syst)F+ < 0.07 @ 95%

C.L. Matrix Element method

cos θ* template fit method

f0 = 0.637 ± 0.084 (stat) ± 0.069 (syst)

Assuming f+=0

Forward Backward Asymmetry 1.9 fb-1

Slightly positive Afb Slightly negative Afb

ttbar production mechanism 2.0 fb-1

Fgg=0.53+0.35-0.37(stat.)+0.07

-0.08(syst.)

q qSpin gg

anti-parallel spin state

Spin

parallel spin state

J = 1 Jz = 1

qq annihilation gg fusion

J = 0 Jz = 0

P P

ll

Fgg = 0.07+0.15-0.07(stat+sys)

1.0 fb-1 Combination

Search for the FCNC top decay 1.9 fb-1

Searching t→Zq vertex in top decay

Br(t→Zq) < 3.7 %

Search For Pair Production of Stop Quarks Mimicking Top Event Signatures

Similar decay product as ttbar

Search for Heavy Top t'->Wq In Lepton Plus Jets Events in 2.8 fb-

1

A Search for charged Higgs in lepton+jets tt-bar events using 2.2 fb-1 of CDF data

etc……